Unfortunately, there's no good or straightforward way to play Garritan Pipe Organs sounds from Finale unless your needs are very simple. (Or at least based on my years of trying/hoping/experimenting.) The Finale/Aria interface is not designed for the stop changes and couplings that organists make all the time. What you can do as a workaround is load the various stops you want to use in the Aria Player slots -- up to 16, each on a different midi channel. Then when you have your music scored, create a separate staff for each stop. Copy the music (or cut and paste) in your many-staff score to reflect what you want each stop to do. For your printed score, hide the extra staves. It's actually easier to create separate grand staves for your manual stops, each grand staff on one channel. It's a shame, because the Garritan sounds are not bad, but they are hard to use. Today I tried Organteq, another pipe organ sound set that came out a few months ago. Although its interface is intuitive like a pipe organ console (yay!), it does not work well with Finale. For example, you cannot turn stops on and off while the Finale file is playing. You can, however, export your Finale file as a midi file and load it into Organtec to make a recording. Setting up the organ and programming the stop changes is still extra work, less so if you have a standalone midi sequencer. But you can do the same with a sequencer controlling the Garritan sounds in Aria Player. And you can make a recording from your midi file in Aria Player. So bottom line is use the Garritan sounds you've already paid for. If you need even more organ sounds, you can buy the Garritan set, or Organteq, or even the more expensive and versatile Hauptwerk. But none will work well with Finale, so expect to do a lot of work to come up with a midi file for decent playback.
Thanks for the comment that explains why extra programming is necessary to get something out of Garritan Pipe Organs sounds or other similar packages. I haven't got time for this extra work, since I've got plenty on my hands already with composing. Something I've just noticed when using the module is that it doen't respond to piano or forte inserts. The volume never changes. Any reason for this, and how to correct it ?
Julian, I'm not sure without checking your file, but suspect the issue is how you try to control volume. Finale's pre-programmed text expressions use key velocity rather than controller 7 (volume). But Human Playback does not interpret them well, so I edit them to use controller 7 instead. (Note some Garritan instruments also use modulation for volume, but for the pipe organ sounds this controller seems to trigger vibrato.) The Controls parameters inside the Aria Player can affect perceived volume, as well as the mixer in Finale. The Finale mixer sets relative volumes for the whole piece, whereas the Aria Player mixer updates in real time. This has been my experience as best I can recall without further investigation. Hope it helps!
I'm just catching up to this - and the lack of pipe organ functionality is a serious shortcoming, considering how many Finale users are church organists or instrumentalists. It would require a special Aria player.
I do it two ways - one of them just as Christopher mentions, with a separate staff for each division; this is, in effect, what is happening when using different divisions. The other method I use is assigning expressions to trigger channel changes - eg, I might have principal 8 and 4 on OM (all channels), and a 2 foot on channel 2 - triggered by a "Prin. 8,4,2" expression that changes the channel to add the octave. I do this when my score has choirs, strings, and / or winds, consuming available rack space for organ voices.
GCPO doesn't respond to dynamics such as cresc, p, or f so you have to play like an unenclosed Baroque instrument (no shutters, crescendo pedal, or pistons): change manuals or add/subtract stops just like Bach. Luckily, text expressions can function as virtual pistons.